The present invention relates to the fabrication of integrated circuits and, more particularly, to a method proton-enhanced diffusion, e.g., diffusion enhanced by the bombardment of ions having a maximum atomic number of two.
Proton-enhanced diffusion has been used in the art to shift P-N and other junctions in planar integrated circuits. U.S. Pat. Nos. 3,718,502, 3,756,862 and 3,761,319 are representative of such proton-enhanced diffusion techniques in the art. In the conventional proton-enhanced diffusion techniques, the P or N type region to be subjected to enhanced diffusion is bombarded with proton (hydrogen) or helium ions at relatively high temperature in the order of more than 450.degree. C for silicon. In these processes, the elevated temperatures are selected so that the drive-in diffusion step, i.e., the driving in or shifting of the junction of the region being bombarded, takes place simultaneously with the bombardment. Thus, the elevated temperature selected must be sufficiently high so that diffusion of the conductivity-determining or dopant ions from the regions being bombarded can take place. While such temperatures are below the normal diffusion temperatures of the particular dopant ions in the particular semiconductor material without such bombardment, nevertheless, the temperatures must be sufficiently high to cause the movement of the dopant ions into substitutional vacancy sites in the surrounding semiconductor material created by the "damaging" bombardment ions. Because elevated temperatures of this order also simultaneously anneal the "damaged" substitutional vacancies, such simultaneous diffusion and bombardment processes have to be conducted under very strict control conditions involving the parameters of diffusivity of the particular dopant ions in the particular semiconductor substrate, temperature, and bombardment dosage. These parameters must be strictly correlated in order to ensure that there are a sufficient number of substitutional vacancies (a factor determined by a combination of anneal rate and bombardment dosage) to accept the number of diffusing dopant ions (a factor determined by a combination of diffusivity and temperature). In addition, such simultaneous processes require higher dosages and higher implant energies to continuously offset the annealing effects.
The strict correlations and controls required in such prior art methods demand highly sophisticated equipment, highly skilled operators or both. While it is recognized, that in certain proton-enhanced diffusion operations, particularly where the movement of the junction or drive-in diffusion has to be within the very exacting dimensional limitations, the prior art techniques may be effective, it would be desirable, if possible, to reduce the need for sophisticated equipment or highly skilled operators where the proton-enhanced diffusion techniques are to be carried out on a large scale in an integrated circuit production line.